Transition metal oxides, such as iron oxide and nickel oxide, are active catalysts for hydrocarbon oxidation. The oxidation products of such a reaction are typically carbon monoxide or carbon dioxide. However, transition metal phosphates, such as ferric phosphate or ferric pyrophosphate, are more selective catalysts for the alkaline oxidative dehydrogenation to olefins. A sol-gel precipitation method, in the liquid phase, is conventionally used to prepare such metal phosphate catalysts. Such a method cannot avoid also forming a certain amount of metal oxide product. Even the presence of a small amount of metal oxide in the desired phosphate catalyst product can be harmful to the selectivity of such a catalyst to the desired olefin product.
In related copending U.S. Ser. No. 192,673, entitled "Oxidative Dehydrogenation of Alkane to Alkene Using a Transition Metal Phosphate Catalyst", filed on even date herewith, abandoned, the catalytic oxidative dehydrogenation of the alkane compound, such as ethane, to the alkene compound, such as ethylene, is carried out using a transition metal phosphate catalyst. The process of this invention is deemed to be one process in which such catalyst materials might be synthesized from the corresponding oxide. In addition, the present process can be used as a convenient way of converting undesired metal oxide materials in conventional transition metal phosphate catalysts to the more desirable phosphate analogue(s). In this manner, the performance of the resulting catalyst composition can be improved (for example, in regard to the selectivity of the catalyst to the desired product of the reaction).